1. Field of the Invention
This invention relates to systems and methods providing a capability for IFF transponder and interrogator functions in addition to ESM/ECM functions, and in particular but not exclusively to such systems and methods for aircraft. Such systems and methods may also find applications in other vehicles for land, air, sea or space use.
2. Discussion of Prior Art
For Air Traffic Control (ATC) purposes, civil and military aircraft are required to be fitted with Identify Friend or Foe (IFF) transponders. These transponders reply automatically, with information such as height, speed, aircraft identification code, when they receive a Radio Frequency (RF) request from a ground stationxe2x80x94usually located at airports.
In times of conflict this identity reporting is used to prevent fratricide and to aid friendly assets in gaining a picture or awareness of the battlespace. In order to prevent enemy forces from exploiting this identity reporting, the interrogation signals are coded or, in the case of more modern systems, encrypted.
A transponder is also required to satisfy civil air traffic control requirements; in this case there are no requirements for coding or encryption other than that the transponder replies with the identify of the aircraft and its current altitude. Military IFF transponders are capable of operating in the civil ATC modes. An emergency mode is also provided which will enable the transponder to act as a distress beacon in the event of pilot ejection or similar emergencies.
A transponder comprises a transmitter/receiver unit, upper and lower transmit/receive antennas and a control unit, as exemplified in FIG. 1 of the accompanying drawings. By international accord, they operate on a transmit frequency band centred on 1090 MHz and a receive frequency band centred on 1030 MHz, and in each case the bandwidth is normally less than 10 MHz.
The military purpose of IFF is identification of friendly aircraft by the use of identification codes on the transmission and reply. In this case, called IFF xe2x80x98Interrogationxe2x80x99, an aircraft can be requested by either a ground station, land/sea vehicle or another aircraft fitted with an Interrogator to reply to a coded request for identification. Only friendly aircraft who know the code of the day can provide the correct response to the Interrogation. On most fighter aircraft the IFF Interrogator, which requires extra xe2x80x98black boxesxe2x80x99 and antennas to those of the IFF Transponder, is often enacted by mounting the IFF Interrogator antennas on the main nose radar dish. In this way, when an aircraft is detected by that radar, it can be selectively interrogated by the directional nose radar dish, without broadcasting the interrogating aircraft""s position through the omnidirectional transmissions typical of Transponder systems. FIG. 2 of the accompanying drawings illustrate a typical such arrangement.
All modern military aircraft have either a Radar Warning Receiver (RWR) or a more capable RWR called Electronic Support Measures (ESM). The purpose of both is to receive, identify and classify RF emissions received at the aircraft; to notify the crew of the direction from which the RF signals came; and, if classified as a xe2x80x98threatxe2x80x99, to enable or initiate appropriate crew warnings and counter measures. Such countermeasures can include RF Electronic Countermeasures (ECM or xe2x80x98jammersxe2x80x99). Most military aircraft especially fighters and bombers, and including helicopters, have ECM capability, either podded (carried under a wing) or internal to the fuselage. FIG. 3 of the accompanying drawings gives a block diagram of a typical fighter ESM/ECM system.
An ESM receiver is essentially a sensitive radio receiver which is rapidly scanned over a wide range of frequencies in order to detect radar signals incident on the aircraft; detected signals are analysed on a pulse by pulse basis to determine, by comparison with a stored library of emitter characteristics, the source of the radar signals. The antenna arrangement associated with the ESM receiver enables the direction from which the signals are arriving to be measured.
The information derived by the ESM receiver is presented graphically to the crew and, if a threat emitter is detected, may be used to cue a jammer or electronic countermeasures (ECM) system to disrupt the operation of the threat. The ECM system consists of an RF transmitter and associated antennas which can be tuned to the frequency of the detected threat and can transmit a variety of complex signals generated by a xe2x80x9ctechniques generatorxe2x80x9d. More recent ECMs are capable of directing the jamming signal towards the threat system in order to maximise their effectiveness.
There is a potential operational problem associated with an IFF transponder as described above due to the fact that transponder signals are broadcast in all directions. The scenario should be considered where a first aircraft is operating covertly and emitting no radio signals in order to minimise the likelihood of an enemy detecting its presence. Another friendly asset, possibly a coalition aircraft or surface based radar, interrogates the first aircraft with a valid IFF signal and its transponder broadcasts its identity thus alerting the enemy to its presence. It should be noted that the enemy do not have to decode the transponder signal in order to detect its presence and, possibly, its bearing. This problem could be averted by the first aircraft suppressing the operation of its transponder; however, this may incur the risk of engagement by the xe2x80x9cfriendlyxe2x80x9d asset and negates the value of having an IFF system in the first place.
We have designed a system in which the IFF Transponder and Interrogator functionality are subsumed within the ESM/ECM equipment. The ESM is used to detect and decode IFF interrogations and to use the associated ECM to transmit the appropriate reply, preferably in the direction of the interrogator. As the replies can be directed specifically towards the interrogator, spurious emissions are minimised, thereby assisting in keep the presence of the aircraft covert. The functionality associated with the IFF decoder and an encryption computer are also preferably incorporated into the ESM and ECM equipment, as well as appropriate interfaces for receiving cryptography information and a control panel.
This system provides significant benefits as a result of the removal of the IFF Transponder and Interrogator boxes and antennas, both for the manufacture of the aircraft and the operator. The system benefits from reduced weight, volume, power and cooling requirements, and cost. The initial and life cycle costs of the aircraft may be reduced, and the system may provide improved aircraft reliability. The aircraft maintenance effort required may also be reduced. The system also provides substantial tactical advantages. Thus the system assists in reducing the electronic signature of the aircraft, giving it improved survivability because of reduced detectability by opposing ground/airborne threat radars. The system also releases space on existing aircraft for other function and/or performance improvements.
Accordingly, in one aspect, this invention provides a radar system for a station, said system comprising:
at least one antenna means for passing signals in the radio frequency waveband;
Identify Friend or Foe (IFF) transponder means for receiving and responding to requests from a remote transmitter via said antenna means;
IFF interrogator means for selectively interrogating in use a remote transmitter via said antenna means;
Radar Warning receiving (RWR) means for processing radio frequency emissions received by said antenna means to identify potential threats; and
Electronic Countermeasure (ECM) means for generating electronic countermeasures signals and for passing said signals to said antenna means for transmission.
The arrangement preferably includes control means for controlling the passage of signals between said IFF transponder means, said IFF interrogator means, said RWR means, said ECM means and said antenna means respectively.
The number, type and configuration of the antennas making up the antenna means may vary widely according to the particular application. Thus the system may comprise separate transmit and receive antennas, and respective separate forward facing and rearward facing sets of one or more antennas may be provided to allow coverage of the forward and rearward hemispheres. The provision of forward and rearward looking transmit antennas gives the ability to perform rear hemisphere IFF interrogation, which is not present in any of the earlier systems described above. This is particularly useful in a military context when the vehicle or station fitted with the system is past the forward edge of the battle area.
The transmit antennas are preferably highly directional or capable of being operated highly directionally so that responses from the IFF transponder are narrow beam, to provide better threat avoidance. The system can also provide, compared with conventional IFF responses, a much finer spatial response to military IFF interrogations, again providing better threat avoidance.
The antenna means may comprise one or more phased array antennas.
The receive antenna means preferably has a direction of arrival performance typically of 1 degree r.m.s. error.
The system may also include navigational and similar apparatus using the same antenna means. Thus said system may include microwave landing systems (MLS) means under the control of said control means and receiving signals from said antenna means. Likewise the system may include distance measuring equipment controlled by said control means, with signals therefor being passed by said antenna means.
Still further, said system may include radio communications apparatus, with signals being passed by said antenna means.
The system preferably also includes means for detecting and displaying IFF requests/responses on display means, and/or for using data identifying said IFF requests/responses for threat assessment.
Whilst the system may be used in a number of different applications e.g. land, air or sea, it has been designed with particular reference to use on board an aircraft. Accordingly the invention extends to an aircraft radar system as defined above and also to aircraft fitted with such a system.
The invention also extends to a method of providing IFF transponder, IFF interrogator, ECM and RWR/ESM facilities for a mobile station, which comprises providing antenna means for transmitting and receiving radiation, passing IFF transponder requests and responses via said antenna means, passing IFF interrogation requests via said antenna means, passing RWR/ESM signals via said antenna means and passing ECM signals via said antenna means.
Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description.